A popular power augmentation system for gas turbines is inlet fogging. In an inlet fogging system, fine droplets of demineralized water are sprayed into the intake duct of the compressor stage of the gas turbine and evaporate and cool the inlet air. The amount of water injected can be controlled to arrive at approximately saturation conditions at the compressor inlet (thus, attaining or nearly attaining the wet bulb temperature) or may include the deliberate injection of a higher amount of water with the specific objective of allowing fine droplets (sized below about 20 microns) to enter the compressor, thus allowing fog intercooling and a further boost of power and improvement of efficiency.
Regardless of the efficiency of the fog nozzles and the atomization process, free water tends to pool on the floor of the duct near the bell mouth of the compressor, and also strike the duct walls, structures within the duct, and the intake cone of the gas turbine compressor. The water that deposits from the fog droplets tends to grow in drop size, or create streams or puddles, and can be suctioned into the compressor as larger drops where it could cause potential erosion damage to the compressor blading.
A current method of avoiding the damage caused by free water is by the use of strategically placed drains that are provided with P-traps or one way flapper valves which essentially will allow water to drain out of the duct when a certain head of water accumulates. A problem with this is that the activation of the trap or flapper will, by definition, call for some collection of water. Thus, prior to the drain activating, some ingestion of water can occur. Further, the currently used drain approach does not address sheets of water on walls or other structures, that are literally sucked into the compressor due to rapid air flow and compressor suction pressure which can be as high as 165 cms of water (below ambient).
The suction pressure of an axial flow compressor may cause sheeting of water on various surfaces surrounding the intake bell mouth including vertical duct walls, the compressor intake cone, the floor of the duct, intake support struts, and the bell mouth. This water then accumulates and is sucked into the compressor. At times it adheres to the intake support struts, or inlet guide vanes (IGVs) and then gets ingested. As the droplet sizes are much larger than the original fog droplets, these ingested droplets can cause blade erosion or other aerodynamic problems. At times severe ingestion can cause casing distortion of the compressor housing and even blade tip deformation.
The invention is focused on minimizing the amount of water that can cause such problems. With the use of inlet washing systems the potential for similar wetting and ingestion of larger droplets exists. This invention can be used for minimizing this problem in addition to fogging applications and may also apply to applications with media evaporative coolers or chillers where large droplets can be formed due to either carryover or by condensation in the duct.